@mhoye this is a great thread, and I agree with all of it except this tangential point.
Matrix moderation tools are a chaotic mess. Some of that is inherent distsys problems, some of that is missing / bad protocol design or poor integration. Not all of it is directly related to moderation being a reactive afterthought, but is compounded by the combination of that with general matrix desync artifacts.
Speaking from experience doing matrix moderation, notably during an especially nasty period a year or two ago, there is plenty of capability left to build. While the more centralised platforms have some inherent advantages here, that's not the only reason their moderation capabilities are easier to operate effectively.
There are tools. Many different variants, even. That they are better than what IRC has is not in dispute, but that's the lowest of low bars.
ETA: The people building the tools are working on the fringes and get easily burned out, for obvious additional reasons beyond all the normal and accelerating reasons everyone else is These Days.